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The Brain’s Growth and Development

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The human brain is large and in charge. It controls everything you do—breathing, eating, reading this sentence. Everything.

Humans have the largest brain for their body size in the animal world. Our closest relatives, chimpanzees, cannot perform tasks beyond those of an average toddler. What makes us so smart?

Whatever it is, it’s not in the brain stem. This part of the brain controls sleeping, heartbeat, and other basic, life-or-death activities. Our brain stem is a lot like the brain stems of reptiles, birds, and other mammals. That makes sense, because all animals need to perform the same life-or-death activities.

It’s not in the cerebellum (ser-i-BELL-um). This part controls movement. Reptiles, birds, and mammals (including us) all move. So our cerebellums are similar. But other animals use much of their brainpower for moving, sensing, and surviving. They have relatively little left for thinking.

It’s in the cerebrum. This wrinkled, squishy mass makes up 85 percent of the human brain’s weight. It’s where we think, reason, compose language, know how to play instruments, and design bridges. In short, it does all those unique things that make us human.